XML Web Services Security

XML Web Services Security March 27, 2003 IIDS Group, Vrije Universiteit Yuri Demchenko, NLnet Labs <demch@NLnetLabs.nl>

Outlines • Historical • XML Security • Web Services Security • OGSA Security • XML Web Services technology for IIDS - Discussion XML Web Services Security

Historical: How all this started(quoting Tim Berners-Lee) • Initial idea to create resource description language • Existing technologies: SGML + WAIS, Gopher + Library Catalogues • Problems: hyperlinks reference and semantic meaning binding • Past steps: • WWW and HTML • RDF and Metadata • XML and XML Signature • Next step: Semantic Web • Ongoing development: Computer Grids -> Information Grids -> Semantic Grids XML Web Services Security

XML Basics: DTD, Schema, XML Protocol, etc. • DTD is document-oriented • Like HTML • Schema is data-oriented • XML Signature • SAML • Basic XML Protocol(s) • XML-RPC • SOAP • XForms, XLink, XML Query, XPath, XPointer, XSL and XSLT, Legal XML XML Web Services Security

XML Security vs Traditional (Network) security • Traditional Security: • Host-to-host or point-to-point security • Client/server oriented • Connection or connectionless oriented • Generically single/common trust domain/association • XML Security • Document oriented approach • Security tokens/assertions and policies can be associated with the document or its parts • Intended to be cross-domain • Potentially for virtual and dynamic trust domains (security associations) XML Web Services Security

XML Security - Components • XML Signature • XML Encryption • Security Assertion • SAML (Security Assertion Mark-up Language) • XrML (XML Right Mark-up Language) • XACML (XML Access Control Mark-up Language) • XKMS (XML Key Management Specification) XML Web Services Security

XML Signature: Features • Fundamental feature: the ability to sign only specific portions of the XML tree rather than the whole document. • XML document may have a long history when different component are authored by different parties at different times • Different parties may want to sign only those elements relevant to them • Important when keeping integrity of certain parts of an XML document is essential while leaving the possibility for other parts to be changed • Allows carrying security tokens/assertions on document/data rather than on user/client • Provides security features for XML based protocols • Provides basic functionality for state assertions XML Web Services Security

XML Signature structure • <Signature ID?> • <SignedInfo> <CanonicalizationMethod/> <SignatureMethod/> (<Reference URI? > (<Transforms>)? <DigestMethod> <DigestValue> </Reference>)+ </SignedInfo> • <SignatureValue> (<KeyInfo>)? (<Object ID?>)* • </Signature> XML Web Services Security

C B D D File/Document Encryption vs XML Encryption • For multi-user encryption Document can contain encrypted shared decryption key with pubK of all intended targets EncryptedFile(pubK B) Only User B can open FileA with pirvK B FileA/Doc FileA/DocA DecryptwithprivK B Encryptwith/for pubK B User B User A(knows pubK B) User B can read whole Doc1 and decrypt only part B Doc1 DecryptwithprivK B XMLDoc1 Encryptselect parts for select targets Encryptedselect parts B Doc1 DecryptwithprivK C User C can read whole Doc1 and decrypt only part D C D User A(knows pubK B,C, D) XML Web Services Security

SigB SigC SigD XMLSigA Binding semantics to the document with XMLSig • XML Signature allows signing selected parts of the document • Providing Integrity and Authenticity • Binding attributes and permissions to the the Document Signed selected parts Signed selected parts Signed selected parts Signed selected parts XMLDoc1/JobDescr SigB SigB SigB SigB SigC SigC SigC XMLSigA SigD SigD XMLSigA XMLSigA XMLSigA XMLSigA • Users/Systems B, C, D sign selected parts with their privK B, C, D • Can add new information and re-sign document User/System Acreates XML Doc1 and signs with SigA Receiver validates integrity of XML Doc1 by validating all signatures XML Web Services Security

XML Web Services • A Web Service is a software system identified by URI, whose public interfaces and bindings are defied and described by XML. Other software systems may discover and interact with the Web Service in a manner prescribed by its definition, using XML based messages conveyed by Internet protocols. • Service oriented architecture for application-to-application interaction • Describing Web services – WSDL • Exchanging messages – SOAP extensions • Publishing and Discovering WS descriptions - UDDI • Programming language-, programming model-, and system software-neutral • Standard based: XML/SOAP foundation • Industry initiatives (and development platforms) • Sun SunONE/J2EE (SunONE Studio) • Microsoft .NET (Visual Studio .NET) • IBM Dynamic e-Business (AlphaWorks) • XML Spy by Altova XML Web Services Security

XML WS - Service Oriented Architecture • WSDL based Service Description • SOAP based messaging over HTTP, SMTP, TCP, etc. • UDDI based Publishing/Discovery XML Web Services Security

Web services features – three stacks XML Web Services Security

Web Service Description Language (WSDL) • WSDL is an XML document format for describing Web service as a set of endpoints operating on messages containing either document-oriented or procedure-oriented (RPC) messages. • The operations and messages are described abstractly and then bound to a concrete network protocol and message format to define an endpoint XML Web Services Security

Web Services Security Model • WS-Security model provides end-to-end security (as contrary to point-to-point) allowing intermediaries • A Web service can require that an incoming message prove a set of claims (e.g., name, key, permission, capability, etc.). • Set of required claims and related information is referred as a Policy. • A requester can send messages with proof of the required claims by associating security tokens with the messages. • Messages both demand a specific action and prove that their sender has the claim to demand the action. • When a requester does not have the required claims, the requester or someone on its behalf can try to obtain the necessary claims by contacting other Web services. • Security token services broker trust between different trust domains by issuing security tokens. XML Web Services Security

Web Services Security Model • Security token types • Username/password • X.509 PKC • SAML • XrML • XCBF XML Web Services Security

WS Security Scenarios • All are built on SOAP based security tokens exchange • Direct Trust using username/password (using SSL/TLS) • Direct Trust using security token • Security token acquisition • Issued security token • Enforcing business policy • Web clients • Mobile clients (gateway services) • Enabling Federations • Using trust chaining, security token exchange, credentials exchange • Supporting delegation • Access control • Auditing XML Web Services Security

WS-SecureConversation WS-Federation WS-Authorisation WS-Policy WS-Trust WS-Privacy WS Security SOAP Foundation Web Services Security Architecture • WS-Security: describes how to attach signature and encryption headers to SOAP messages. In addition, it describes how to attach security tokens, including binary security tokens such as X.509 certificates, SAML, Kerberos tickets and others, to messages. • Core Specification - Web Services Security: SOAP Message Security • http://www.oasis-open.org/committees/download.php/1043/WSS-SOAPMessageSecurity-11-0303.pdf XML Web Services Security

Web Service Security – others specifications • WS-Policy: will describe the capabilities and constraints of the security (and other business) policies on intermediaries and endpoints (e.g. required security tokens, supported encryption algorithms, privacy rules) • WS-Trust: will describe a framework for trust models that enables Web services to securely interoperate • WS-Privacy: will describe a model for how Web services and requesters state privacy preferences and organizational privacy practice statements • WS-SecureConversation: will describe how to manage and authenticate message exchanges between parties including security context exchange and establishing and deriving session keys • WS-Federation: will describe how to manage and broker the trust relationships in a heterogeneous federated environment including support for federated identities • WS-Authorization: will describe how to manage authorization data and authorization policies XML Web Services Security

WS Security: SOAP Message Security • SOAP Message Security must support a wide variety of security models. • Key driving requirements for the specification: • Multiple security tokens for authentication or authorization • Multiple trust domains • Multiple encryption technologies • End-to-end message-level security and not just transport-level security • Primary security concerns • Protection against interception – confidentiality • XML Encryption • Protection against illegal modification – integrity • XML Signature • Security consideration – Auditing • Timestamping and message expiration • Sequence number and Messages correlation XML Web Services Security

SOAP Message Security Model • Describe abstract message security model in terms of security tokens combined with digital signatures as proof of possession of the security token (key). • Security token asserts claims and signatures provide mechanism for proving the sender’s knowledge of key • A claim can be either endorsed or unendorsed by a trusted authority • An X.509 Cert, claiming the binding between one’s identity and public key, is an example of a endorsed/signed security token • An unendorsed claim can be trusted if there is trust relations between the sender and the receiver (usually based on historical relations/communications context) • Proof-of-Possession (e.g. username/password) – special type of unendorsed claim XML Web Services Security

SOAP Header SOAP Routing Security token Digital signature DigSignature description:Normalisation Transformation Signed elements DigSignature value Ref to DSign Sec token SOAP Message payload WS-Security SOAP message structure • URI: http://schemas.xmlsoap.org/ws/2002/04/secext • Namespaces used in WSSL: • SOAP S http://www.w3.org/2001/12/soap-envelope • XML Digital Sign ds http://www.w3.org/2000/09/xmldsig# • XML Encryption xenc http://www.w3.org/2001/04/xmlenc# • XML/SOAP Routing m http://schemas.xmlsoap.org/rp • WSSL wsse • http://schemas.xmlsoap.org/ws/2002/04/secext • Security element • Header block targets specific receiver SOAP Actor • Multiple header blocks are allowed targeted at different Actors • New header block are added/appended to existing ones XML Web Services Security

SecurityTokenReference Model • Usage and processing models for the <wsse:SecurityTokenReference> element. • Local Reference – A security token, that is included in the message in the <wsse:Security> header, is associated with an XML Signature. • Remote Reference – A security token, that is not included in the message but may be available at a specific URI, is associated with an XML Signature. • Key Identifier – A security token, which is associated with an XML Signature and identified using a known value that is the result of a well-known function of the security token (defined by the token format or profile). • Key Name – A security token is associated with an XML Signature and identified using a known value that represents a "name" assertion within the security token (defined by the token format or profile). • Format- Specific References – A security token is associated with an XML Signature and identified using a mechanism specific to the token • Non-Signature References – A message may contain XML that does not represent an XML signature, but may reference a security token (which may or may not be included in the message). XML Web Services Security

Computer Grids • Originated from Distributing Supercomputing • To become “pluggable” computing resource • Computer Grids -> Information Grids -> Semantic Grids • Current de-facto standard – Globus Toolkits • Open Grid Services Architecture was boosted by developing XML Web Services – 2002 • Commercial Grids are starting XML Web Services Security

Open Grid Services Architecture (OGSA) • WSDL extensions to describe specifics of Grid Services • Defines new portType - GridService • Provides mechanism to create Virtual Organisation • Provides mechanism to create transient services - Factories • Provides soft-state registration of GSH - Registry • Grid services can maintain internal state for the lifetime of the service. The existence of state distinguishes one instance of a service from another that provides the same interface. • OGSA services can be created and destroyed dynamically • Grid Service is assigned globally (persistent) unique name, the Grid service handle (GSH) • Grid services may be upgraded during their lifetime and referenced by Grid (dynamic) service reference (GSR) XML Web Services Security

Security Issues in Grid computing - Specifics • General issues: • Traditional systems are user/client/host centric • Grid computing is data centric • Traditional systems: • Protect system from its users • Protect data of one user from compromise • In Grid systems: • Protect applications and data from system where computation execute • Stronger/mutual authentication needed (for users and code) • Ensure that resources and data not provided by a attacker • Protect local execution from remote systems • Different admin domains/Security policies XML Web Services Security

Security Issues in Grid computing - Components • Authentication • Password based • Kerberos based (authentication and key distribution protocol) • SSL authentication • PKI/Cert based • Authorisation • Integrity and confidentiality • Cryptography • Assurance • Accounting • Audit XML Web Services Security

Authentication • Traditional systems: • Authenticate user/client to protect system • Grid systems: • Mutual authentication required • Ensure that resources and data not provided by a attacker • Delegation of Identity • Process that grants one principal the authority to act as another individual • Assume another’s identity to perform certain functions • E.g., in Globus: use gridmap file on a particular resource to map authenticated user user onto another’s account, with corresponding privileges • Data origin authentication XML Web Services Security

Authorisation • Traditional systems: • Determine whether a particular operation is allowed based on authenticated identity of requester and local information • Grid systems: • Determine whether access to resource/operation is allowed • Access control list associated with resources, principal or authorised programs • Distributed Authorisation • Distributed maintenance of authorisation information • One approach: Embed attributes in certificates • Restricted proxy: authorisation certificate that grants authority to perform operation on behalf of grantor • Alternative: separate authorisation server XML Web Services Security

Assurance, Accounting, Audit • Assurance • When service is requested, to assure that candidate service provider meets requirements • Accounting • Means of tracking, limiting or changing for consumption of resources • Audit • Record operations performed by systems and associate actions with principals • Find out what went wrong: typical role of Intrusion Detection Systems XML Web Services Security

OGSA Security • Built upon WS Security XML Web Services Security

OGSA Security Roadmap - Specifications (1) • Naming • OGSA Identity Specification • OGSA Target/Action Naming Specification • OGSA Attribute and Group Naming Specification • Transient Service Identity Acquisition Specification • Translating between Security Realms • Identity Mapping Service Specification • Generic Name Mapping Specification • Policy Mapping Service Specification • Credential Mapping Service Specification • Authentication Mechanism Agnostic • Certificate Validation Service Specification • OGSA-Kerberos Services Specifications • Pluggable Session Security • GSSAPI-SecureConversation Specification XML Web Services Security

OGSA Security Roadmap - Specifications (2) • Pluggable Authorization Service • OGSA-Authorization Service Specification • Authorization Policy Management • Coarse-grained Authorization Policy Management Specification • Fine-grained Authorization Policy Management Specifications • Trust Policy Management • OGSA Trust Service Specification • Privacy Policy Management • Privacy Policy Framework Specification • VO Policy Management • VO Policy Service Specification • Delegation • Identity Assertion Profile Specification • Capability Assertion Profile Specification XML Web Services Security

OGSA Security Roadmap - Specifications (3) • Firewall "Friendly" • OGSA Firewall Interoperability Specification • Security Policy Expression and Exchange • Grid Service Reference and Service Data Security Policy Decoration Specification • Secure Service Operation • Secure Service’s Policy and Processing Specification • Service Data Access Control Specification • Audit and Secure Logging • OGSA Audit Service Specification • OGSA Audit Policy Management Specification XML Web Services Security

Trust establishment process (1) • 1. Binding an entity identity to a Distinguished Name (“DN” - the subject name in an X.509 identity certificate) • Trust in this step is accomplished through the (published and audited) policy based identity verification procedures of the Certification Authority that issues the identity certificates • 2. Binding a public key to the DN (generating an X.509 certificate) • Trust in this step is accomplished through the (published and audited) policy based operational procedures of the issuing Certification Authority (“CA”). • 3. Assurance that the public key that is presented actually represents the user • Trust in this step comes from the cryptography and protocols of Public Key Infrastructure. • 4. Assurance that a message tied to the entity DN could only have originated with that entity: • Trust that a message signed by a private key could only have been signed by the private key corresponding to the public key (and therefore the named entity via X.509 certs) comes from public key cryptography • Trust in this step is also through user key management (the mechanism by which the user limits the use of its identity), which is assured by user education, care in dealing with one’s cyber environment, and shared understanding as to the significance of the private key. XML Web Services Security

Trust establishment process (2) • 5. Mutual authentication, whereby two ends of a communication channel agree on each other’s identity • Trust in this step is through the cryptographic techniques and protocols of the Transport Level Security (“TLS”) standard. • 6. Delegation of identity to remote Grid systems • Trust in this step is through the cryptographic techniques and protocols for generating, managing, and using proxy certificates that are directly derived from the CA issued identity certificates. XML Web Services Security

Remote Authentication, Delegation, and Secure Communication in GRID • Remote authentication is accomplished by techniques that verify a cryptographic identity in a way that establishes trust in an unbroken chain from the relying party back to a named human, system, or service identity. This is accomplished in a sequence of trusted steps, each one of which is essential in order to get from accepting a remote user on a Grid resource back to a named entity. • Delegation involves generating and sending a proxy certificate and its private key to a remote Grid system so that remote system may act on behalf of the user. This is the essence of the single sing-on provided by the Grid: A user / entity proves its identity once, and then delegates its authority to remote systems for subsequent processing steps. • A secure communication channel is derived from the Public Key Infrastructure process and the IETF Transport Level Security protocol. XML Web Services Security

Globus Grid Security Infrastructure (GSI) • Operational solution providing security infrastructure for Globus Toolkits • Targeted problems: • Thousands of users – thousands of Certs – many of CAs (with different policies) • Grid-wide user group and roles are needed • No grid-wide logging or auditing • Need for anonymous users • Intended to evolve into OGSA Security • GSI Components • Proxy Certificate Profile • Provides proxy credentials to allow for single sign-on and to provide delegated credentials for use by agent and servers • Online Credential Retrieval to create and manage proxy certificates • Impersonation certificate and restricted delegation certificate XML Web Services Security

Proxy Certificate Profile • Impersonation – used for Single-Sign-On and Delegation • Unrestricted Impersonation • Restricted Impersonation defined by policy • Proxy with Unique Name • Allows using in conjunction with Attribute Cert • Used when proxy identity is referenced to 3rd party, or interact with VO policy • Proxy Certificate (PC) properties: • It is signed by either an X.509 End Entity Certificate (EEC), or by another PC. This EEC or PC is referred to as the Proxy Issuer (PI). • It can sign only another PC. It cannot sign an EEC. • It has its own public and private key pair, distinct from any other EEC or PC. • It has an identity derived from the identity of the EEC that signed the PC. • Although its identity is derived from the EEC's identity, it is also unique. • It contains a new X.509 extension to identify it as a PC and to place policies on the use of the PC. This new extension, along with other X.509 fields and extensions, are used to enable proper path validation and use of the PC. XML Web Services Security

Reference: PKC vs AC: Purposes • X.509 PKC binds an identity and a public key • AC is a component of X.509 Role-based PMI • AC contains no public key • AC may contain attributes that specify group membership, role, security clearance, or other authorisation information associated with the AC holder • Analogy: PKC is like passport, and AC is like entry visa • PKC is used for Authentication and AC is used for Authorisation • AC may be included into Authentication message • PKC relies on Certification Authority and AC requires Attribute Authority (AA) XML Web Services Security

X.509 PKC Version Serial number Signature Issuer Validity Subject Subject Public key info Issuer unique identifier Extensions AC Version Holder Issuer Signature Serial number Validity Attributes Issuer unique ID Extensions PKC vs AC: Certificates structure XML Web Services Security

X.509 PKC Fields Serial Number Subject Subject Public Key Issuer Unique ID Subject Unique ID X.509 PKC Extensions Standard Extensions Authority Key Identifier Subject Key Identifier Key Usage Extended Key Usage CRL Distribution List Private Key Usage Period Certificate Policies Policy Mappings Subject Alternative Name Issuer Alternative Name Subject Directory Attributes Basic Constraints Name Constraints X.509 PKC Fields and Extensions – RFC 3280 • X.509 PKC Fields • Private Extensions • Authority Information Access • Subject Information Access • Custom Extensions XML Web Services Security

AC Attribute Types Service Authentication Information Access Identity Charging Identity Group Role Clearance Profile of AC AC Extensions Audit Identity To protect privacy and provide anonymity May be traceable via AC issuer AC Targeting Authority Key Identifier Authority Information Access CRL Distribution Points AC Attribute Types and AC Extensions XML Web Services Security

Other Technologies to look for IIDS • SIP (Session Initiation Protocol) based technologies • Instant Messaging and Presence Protocol – SIP based XML Web Services Security

XML Web Services technologies for IIDS • Discussion XML Web Services Security

XML Web Services Security